There is conventionally proposed an optical scanning apparatus such as a laser scanning module that performs a two-dimensional scan of a laser light emitted from an RGB (Red Green Blue) light source using an MEMS (Micro Electro Mechanical Systems) mirror, and draws a predetermined image on a screen.
Such an optical scanning apparatus includes: a mirror; support beams that support both opposite sides of the mirror; a resonance driver part that supports the mirror via the support beams; and a compulsive driver part that supports the resonance driver part. The optical scanning apparatus rotates the mirror about two axes that are orthogonal to each other by applying the voltage to piezoelectric films that are provided to the resonance driver part and the compulsive driver part, thereby allowing the two-dimensional scan of the image formation position using the mirror.
The rotation of the mirror by the compulsive driver part is slower than the rotation by the resonance driver part. The waveform of the voltage applied to the piezoelectric films provided to the compulsive driver part is formed to be a sawtooth waveform. The resonance composition contained in the higher harmonic wave having this sawtooth waveform causes the resonance vibration of the mirror; this sometimes poses the unnecessary vibration called ringing.
The frequency of the resonance composition causing the ringing changes depending on the temperature, the acceleration applied to the mirror, or the deterioration of the mirror. In addition, the frequency changes sharply and rapidly, e.g., when the optical scanning apparatus is mounted in a vehicle.
The frequency components leading to the ringing thus need to be removed from the drive signal by detecting the ringing state, e.g., the resonance frequency of the ringing, while driving the optical scanning apparatus. For instance, Patent literature 1 describes an optical deflector that detects the frequency components causing the ringing by analyzing frequency components with FFT of the data acquired by the frequency sweep of the drive signal, and eliminates the detected frequency components from the drive signal with a filter.